There have been previous attempts to provide catalysts containing certain metal oxides and mixed metal oxides alone and in combination with noble metals or their oxides for the oxidation of carbon monoxide to carbon dioxide. There have also been previous attempts to provide methods for the manufacture of such catalysts. These attempts have not produced catalysts having certain advantages as discussed below.
For example, GB 2 221 852A describes vehicle exhaust gas catalysts formed from mixed oxide compositions of tin(IV) oxide, SnO.sub.2 and either or both of a cobalt oxide, preferably Co.sub.3 O.sub.4, and manganese(IV) oxide, MnO.sub.2. However, these catalysts show no activity for the oxidation of carbon monoxide at temperatures less than about 50.degree. C., and exhibit maximum catalytic activity at temperatures above about 140.degree. C. Moreover, the methodology taught in GB 2 221 852A includes final calcination of the catalyst at temperatures sufficiently high, e.g. , 600.degree. C., so as to deactivate the catalyst with respect to the lower oxidation temperatures desired for use of such catalysts.
U.S. Pat. No. 3,909,455 describes a catalyst for the oxidation of carbon monoxide at ambient conditions utilizing a high surface area alumina support containing less than about 15 weight percent cobalt deposited thereon. These catalysts were blue in color, thereby containing all of their cobalt exclusively in a tetrahedrally coordinated divalent form, CoAl.sub.2 O.sub.4, a distinct crystalline phase. It was indicated that when the cobalt content of their catalyst exceeded 15 percent by weight the color of the product became black (containing cobalt in two oxidation states, II and III, i.e., Co.sub.3 O.sub.4) and did not show catalytic activity.
Laid Open Patent Publication No. Sho 50/1975-36387 discloses a catalytic filter for air purification utilizing manganese oxide on a net-like structural body. Other oxides of copper, cobalt and silver may also be utilized in combination with at least 50 mole percent manganese oxide on the net-like structural body.
The search has continued for a catalyst active at lowered, e.g., ambient, temperatures substantially free of the disadvantages, defects and limitations of prior materials.